[clangd] Introduce PostingList interface

This patch abstracts `PostingList` interface and reuses existing
implementation. It will be used later to test different `PostingList`
representations.

No functionality change is introduced, this patch is mostly refactoring
so that the following patches could focus on functionality while not
being too hard to review.

Reviewed By: sammccall, ioeric

Differential Revision: https://reviews.llvm.org/D51982

llvm-svn: 342155

1 files changed, 84 insertions, 0 deletions

diff --git a/clang-tools-extra/clangd/index/dex/PostingList.cpp b/clang-tools-extra/clangd/index/dex/PostingList.cpp
new file mode 100644
index 00000000000..99e534d1a7f
--- /dev/null
+++ b/clang-tools-extra/clangd/index/dex/PostingList.cpp
@@ -0,0 +1,84 @@
+//===--- PostingList.cpp - Symbol identifiers storage interface -----------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#include "PostingList.h"
+#include "Iterator.h"
+
+namespace clang {
+namespace clangd {
+namespace dex {
+
+namespace {
+
+/// Implements Iterator over std::vector<DocID>. This is the most basic
+/// iterator and is simply a wrapper around
+/// std::vector<DocID>::const_iterator.
+class PlainIterator : public Iterator {
+public:
+  explicit PlainIterator(llvm::ArrayRef<DocID> Documents)
+      : Documents(Documents), Index(std::begin(Documents)) {}
+
+  bool reachedEnd() const override { return Index == std::end(Documents); }
+
+  /// Advances cursor to the next item.
+  void advance() override {
+    assert(!reachedEnd() &&
+           "Posting List iterator can't advance() at the end.");
+    ++Index;
+  }
+
+  /// Applies binary search to advance cursor to the next item with DocID
+  /// equal or higher than the given one.
+  void advanceTo(DocID ID) override {
+    assert(!reachedEnd() &&
+           "Posting List iterator can't advance() at the end.");
+    // If current ID is beyond requested one, iterator is already in the right
+    // state.
+    if (peek() < ID)
+      Index = std::lower_bound(Index, std::end(Documents), ID);
+  }
+
+  DocID peek() const override {
+    assert(!reachedEnd() &&
+           "Posting List iterator can't peek() at the end.");
+    return *Index;
+  }
+
+  float consume() override {
+    assert(!reachedEnd() &&
+           "Posting List iterator can't consume() at the end.");
+    return DEFAULT_BOOST_SCORE;
+  }
+
+  size_t estimateSize() const override { return Documents.size(); }
+
+private:
+  llvm::raw_ostream &dump(llvm::raw_ostream &OS) const override {
+    OS << '[';
+    if (Index != std::end(Documents))
+      OS << *Index;
+    else
+      OS << "END";
+    OS << ']';
+    return OS;
+  }
+
+  llvm::ArrayRef<DocID> Documents;
+  llvm::ArrayRef<DocID>::const_iterator Index;
+};
+
+} // namespace
+
+std::unique_ptr<Iterator> PostingList::iterator() const {
+  return llvm::make_unique<PlainIterator>(Documents);
+}
+
+} // namespace dex
+} // namespace clangd
+} // namespace clang